Regarding GameGuard, if previously you launched TO fine...and when you wanted to start TO again [after you closed down, and restart TO], and you got that error, probably the best way you do is to restart the computer, so GameGuard won't stay in memory [that's why sometime it says "restart computer", "failed to initializes"..etc]. You closed TO in Task Manager only closed the game, not the GameGuard.
Also, GameGuard can't be "end task" normally by using Task Manager, since it's a rootkit. You might want to use Windows Sysinternal to check on extra hidden processes in your computer.
- Windows Sysinternals: Documentation, downloads and additional resources